Drop generator with rotatable transducer

ABSTRACT

A drop generator in which a working fluid is forced through orifices in a flexible plate mounted on the drop generating head. The resulting filaments of working fluid break down into drops and the size and spacing of the drops are regulated by propagating a series of bending waves down the length of the orifice plate. The waves are propagated by means of an ultrasonic transducer mounted for rotation about its axis on the drop generator and directly contacting the orifice plate. Fine control over the exact point of contact between the tip of the transducer and the orifice plate is attained by forming the tip offset with respect to the axis of the transducer and rotating the transducer about its axis.

'United States Patent Houser r 1 a [54] DROP GENERATOR WITH ROTATABLETRANSDUCER [72] Inventor: Philip H. Houser, Chillicothe, Ohio [73]Assignee: The Mead Corporation, Chillicothe,

Ohio

22 Filed! on. 14, 1971 21 Appl.No.:189 ,296

[52] U.S.Cl. .....239/l02,139/15,?46/75 51 111 .01. ..ll05b3ll4 581Field of Search.....346ll, 75; 140; 317 3; 239/3, 239/15,4, 102

[56] References v Q UNITED STATES PATENTS 3,577,198 5/1971 Beam...'........346/75 3,656,174 4/1972 Robertson .,..,.346/75 1 51 Oct. 31,1972 Primary Examiner-Joseph W. Hartary Attorney-Lawrence B. Biebel eta1.

[ ABSTRACT A drop generator which a working fluid is vforced throughorifices in a flexible plate mounted on the drop generating head. Theresulting filaments of workin'g fluid break down into drops and the sizeand spacing of the drops are regulated by propagating a series ofbending waves down the length of the orifice plate. The waves arepropagated by means of an ultrasonic transducer mounted for rotationabout its axis on thedrop generator and directly contacting the orifice.plate'.;Fine control overthe exact point of contact between the tip ofthe transducer and the orifice plate is attained by forming the tipoffset with respect to the axis of the transducer and rotatingthetransducer about its axis.

8 Claims, 5 Drawing Figures PATENIED nor a 1 I972 SHEET 1 [IF 2 w llPATENTED UB1 31 I972 SHEET 2 or g FIG-2 "FIG-3.

I '1 .1. DROPGENERATORWITH ROTATABLE TRANSDUCER"-CROSS-REFERENCETO:RELATE APPLICATIONS Reference ismade-to copendingpatent "applications TWIN ROW DROP GENERATOR, Ser. No. 189,298

and APPARATUS AND METHOD FOR GENERA- TlON OF DROPS, Ser. No.; 189,297filed on an even date herewith and assigned to the same assignee-as thepresent'invention.

BACKGROUND OFTPTE lNVENTlON This invention relatesgenerally' to thefield of fluid drop generation and the application thereof to jet droprecorders of the type shown in Sweet et al.-U.S. Pat. No. 3,373,437. andTaylor et al. US. Patent No. 3,560,641. lnrecorders of this type'there.are one or streams and thereafterdepositing at least some of the dropson a moving web of paper or other material.

The abovementioned charging is accomplished by There is a second andmore serious difficulty with the above mentioned prior art stimulationsystems. This is an acoustical cancellation and reinforcement phenomenonwhich causes unpredictable stream-tostream variation in stimulationenergy amplitude. Such ment it is necessary that there be some chargeelectrode surface in the vicinity of the .drop breakoff point.

Thus item be seen that the above mentioned filament application ofcontrol signals to, charging electrodes positioned near each'of thestreams. As eachdrop breaks off: from its-parent fluid filament,itcarries with it a charge which isin effect a sample of the voltagepresent on the associated charge electrode at the instant ofdrop-separation. Thereafter the drop passes through an electrostaticfield and isjdeflected in the field direction a distance whichisproportional to' the magnitude of the'drop charge. In a preferredembodiment the drops are charged binarily forprint-no.-print operation;some drops being uncharged and un deflected for printing, and all otherdrops being charged to a fixed level and deflected into. a catcher. I

In order to accomplish. reproduction with recorders:

of the above described type it isnecessary to control drop formationwith a great dealgof precision. Leftto natural stimulating disturbances,the streams would break; up erratically into drops of various sizes.- atirregular intervals .to.produce a recording which at bestwould be a poorsample of the input control voltages.

Accordingly it is; customary to apply a fixed frequency,

lengthvariations result in a requirement for a very long electrode;something which is difficult to implementin tightly packed arrays of thetype here concerned.

Moreover these length-variations produce a relatively large droppositional placement error. V

This error arises from channel to channel differences in drop flighttime; that is, the elapsed time from drop breakoff/charging to impact onthe moving web of paper. It is somewhat analogous to a gunnery problemwherein a projectile must be aimed to. hit a moving target. l-lere eachdrop is programmed to hit the paper at a precise position relative toother drops, and if it must fallv a greater or lesser distance than hadbeen anticipatedit will miss-With a web speed adjusted for slightoverlap of adjacent printed dots, the above mentioned length differenceof plus or minus 3 times the drop spacing distance will produceaprinting error in the direction of web movement of plus or minus about 3printed dot diameters. Such an error is unacceptably large for printingof graphic arts quality.

In the above noted, related application, AP:

PARATUS AND METHOD FOR GENERATION OF DROPS, the stimulation of the fluidstreams is attained tion, it is important to obtain stimulating bendingwaves constant magnitude stimulating, disturbance. to all of the fluidstreams. This resultsv in trains of uniformly sized and regularly spaceddrops and enables reasonably good sampled data recording.

Various. types of 1 magnetostrictive and piezoelectric transducershavebeenproposed for fluidstream stimulation, and for multiple channeloperationthe transducer may be coupled to the structure of the fluidmanifold as shown in .the. above mentioned-Sweet et al.

patent orv to a fluid supply line as shown in Taylor etal.

Unfortunately these prior art systems stimulate drop of exactly theright mode to obtain stimulation of the desired quality. One of thevariables affecting the characteristics of the waves propagated is thepoint on the surface of the orifice plate where the transducer probemakes contact.

Under ideal circumstances the probe will contact the orifice plate alongthe center-line thereof and produce bending waves for stimulation asdesired. However, it has been found that fully assembled jcoating headswith their attendant tolerance errors and other unpredictable variablesoften times fail to stimulate v properly.

Further it has been observed that this condition may be corrected byfine. adjustment of the contact point between the transducer probe andthe orifice plate. It is an object of this invention to provide a simpleand practical means for such post-assembly adjustment.

. SUMMARY OF THE INVENTION plate can be attained to compensate foranyrvariation between the actual and theoretical contact point.

Thus, the tip of the transducer probe is formed with a point offset withrespect to the axis of the transducer,

and means are provided for mounting the transducer on the generator forrotation about its axis. In this way the exact point of contact will beshifted as the transducer is rotated about its axis.

' BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is an exploded head assembly;

FIG. 2 is across sectional'through the assembly of perspective view of arecording 'FIGJ; I

FIG. 3 is a cross sectional view through a portion of the assembly ofFIG. 1;

FIG..4 is a view of the transducer probe; and FIG. 5 is a bottom view ofthe probe of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS I clamp rods 16.

The recording head'comprises an orifice plate 18 soldered, welded orotherwise bonded to fluid supply manifold 20 with a pair of wedgeshapedacoustical dampers= 22 therebetween. Orifice plate 18 is preferablyformed of a relatively stiff material such as stainless steel or nickelcoated beryllium-copper but is relatively thin' to provide the requiredflexibility.

.Preferably dampers 22 are cast in-place by pouring 58 and 60 reachthrough apertures 62 and 64, respectively, in charge ring plate 50 tosupport holders 56 "without stressing or constraining charge ring plate50.

Deflection ribbon 52 isvalso supported by holders 56 and is stretchedtightly therebetween by means of "tightening blocik 66. Ribbon 52extends between 56, and urging them mutually'inward with a pair ofelastic bands 70. Adjusting blocks 72 are inserted upwardly throughrecessed 74 and 76 to bear against faces 78 of catchers 54, andadjusting screws 80 are provided to drive adjusting blocks 72 andcatchers 54 outwardly against elastic bands 70. Holders 56 are'reinforced plastic board.

The fully assembled recording head is shown in cross section in FIG. 2.As therein illustrated coating fluid 82 flows downwardly throughorifices 26 forming two made of insulative material whichmay be anyavailable rows of streams which break up into drops 84. Drops 84 thenpass through two rows of charge rings 86 in charge ring plate 50 andthence into one of the catchers 54 or onto the moving web of paper 88.Switching of drops between catch and deposit trajectories isaccomplished by electrostatic charging and deflection as hereinafterdescribed. Coordinated printing capability is achieved by staggering thetwo rows of streams in accordance with the teaching of Taylor et al.U.S. Pat. No; 3,560,640. As taught in that patent, the drops in theforward row of steams (i.e: the row most advanced polyurethane rubber orother suitable damping material through openings 24 while tiltingmanifold 20 (orifice plate- 18 being attached) at an appropriate anglefrom the vertical. This is a two step operation as dampers 22.requiretilting in opposite directions.

Orifice plate 18 preferably contains two rows of orifices 26 and isstimulated by a stimulator 28 which is mounted on the recording head andcarries a probe 30 through the manifold 20 and into direct contact withplate 18. The exact construction of the stimulator and related elementsis discussed in detail below. Orifice plate 18, manifold 20, and clampbar 14 together with a filter plate 32 and O -rings 34, 36, and 38 (seealso FIG. 2) comprise a clean package which may be preassembled and keptclosed to prevent dirt or foreign material from reaching and cloggingorifices 26. Conduit 40 may be provided for flushing of the cleanpackage. Service connections for the recording head include a coatingfluid supply tube 42, air exhaust and inlet tubes 44 and 46, and a tube-48 for connection to a pressure transducer (not shown).

Other majorelements comprising the recording head in the direction ofweb movement) are switchedv me time reference framedelayed from that ofthe rear row by a time d/V where d is the row'spacing and V is the webspeed. This produces a coherence such that the two' rows of streamsfunction as a single row with aneffectivev stream spacing equal to halfthe actualfsp'acing in either of the real rows. I

, Formation of drops 84 is closely. controlled by application of aconstant frequency, controlled amplitude, stimulating disturbance .toeach of the fluid streams emanating from orifice plate 18.Distu'rbancesfor this purpose are set up by operating stimulator 28 tovibrate probe 30 at constant amplitude and frequency against plate 18.As described in detail in the above noted, related application,APPARATUS AND METHOD FOR GENERATION OF DROPS, this causes a continuingseries of bending waves to travel the length of plate 18; each waveproducinga drop stimulating disturbance each time it passes one of theorifices 26. Dampers 22 prevent reflection and repropagation of thesewaves. Accordingly each stream comprises an unbroken fluid filament anda series of uniformly sized and regularly spaced drops all in accordancewith the well known Rayleigh jet'break-up phenomenon.

As each drop 84 if formed it is exposed to the charging influence of oneof the charge rings 86. If the drop is to be deflected and caught, anelectrical charge is applied to the associated charge ring 86 during theinstant of drop formation. This causesan electrical charge to be inducedin the tip of the fluid filament and carried away by the drop. A staticelectrical field is set up between deflection ribbon 52 and the faces ofeach of the catchers 54 (by opposite polarity electrical chargngthereof),and when the deflected to'strike the face of the-appropriatecatcher. Thereafter the drop runs downthe face of the catcher,

drop traverses this field it is is ingested, and carried off. Dropingestion may be Appropriate :charges {for accomplishment of the abovementioned drop charging-are induced by setting up an electricalpotential difference between] orifice plate18 (or any other conductivestructure inelectrical contact with thecoating fluidsupply) and eachappropriate charge ring .86. =Thesepotential differences are created bygrounding plate ,18 and applying appropriately timed voltage pulses towires 92 in connectors 94 (only one connector illustrated). Connectors94 areplugged into-receptacles 96zat the :edge of cl-large ring piate 50and deliver the mentioned voltage. pulses over printed circuit lines-98to charge rings'86.-Charge ring plate 50 is fabricated of insulativematerial and charge rings 86 are merely coatingsof conductive materiallining thev surfaces of orifices in the'charge ring plate. Voltagepulses for the'above purpose maybe generated by circuits of thetype-disclosedin Taylor et y al, and wires 92 receiving thesepulsesmaybematched with charge rings'86 on a one-to-onebasis. Alternatively thevoltage pulses may be multiplexed to decrease the number of wires andconnectors. Forsuch an alternative embodiment solid statedemultiplexing'ci'rcuits may be employed to demultiplex the'signals androute the pulses to the proper-charge rings. Such solidstate circuitsmay be manufactured by known methods as a permanent part of charge ringplate 50.

' The'printing head .as abovedescribed is adapted to be employed incombination ,with another such head further inaccordance with theteachings of Taylor et al. Such a vvcombination will produce solidprinting coverage with the streams in each-row on l6-mil-.centers, whichis within the state of the art for current orifice plate and chargering. :plate manufacturing techniques. The effective stream spacing 'forthe equivalent single row is 4 mils, and this will produce solidprinting coverage ifjeach drop makes aflprinted dot in the order ofabout 5 mils. Suitable drops for such printed dots may be produced with"1.5 mil orifices, a fluid pressure of about 11 psi. and a stimulationfrequency of about 60 KHz. To achieve similar solid coverage in thedirection of web travel the speed of web 88 shouldbe set at about, 1,200 ft. per sec. Y

. Unexpectedly it has'been found that solid printing coverage .may beobtained by operating a single printing head as above described but at areduced web travel speed. In particular, a web speed of about 450 ft.per sec. has been found to be satisfactory. This reduction in web speedresults in a decreased longitudinal (i.e. web movement direction)spacing of drop deposit points. In fact when two consecutive drops inone stream are both deposited they tend to pile up and spread in alldirections. They behave much like one drop of larger volumeyand theyfill the laterally adjacent marking cell left empty by omission of thesecond recording head. This, of course, degrades the resolution ofthe-resulting print, but a recording head has been saved. For operationin such a mode it is necessary to slow down charge is applied to Idirection. Thus a signal which would cause catching of .(orpermitdeposition of) one drop in the faster two -head systemis stretched tocatch on the-average about 2.7 drops in the single head system. Catchingor deposition of a single drop is not meaningful for the above-mentioned single head recorder unless it is desired to make gray scalereproductions as taught for instance in Sweet et al. US. Pat. No.3,373,437. i

As noted above it is desirableto be able to provide for preciseadjustment of the point of contact between the'probe 30 and the surfaceof the orifice plate 18. --Such adjustment is-provided in accordancewith the practice of this invention by utilizing a probe with an offce'nter point and a rotatable mounting,'the details of which aredescribed below. Initial placement of the ,probe'pointfor'apprjoximately correct contactis accomplished by mounting stimulator28 in support'bar '12 asillus'trated. The nominal contact area willordinarily be along the center-line of orifice plate 18.

Thus, as best-seen in FIG. 3 of the drawings, the -tra.nsducer130 isreceived in an elongated hollow casing 100 which'in turn ispress fittedinto a cap 102. Cap 102 has integrally formed therewith a reducedportion 104, threaded on its exterior surface, as at 106. Transducer 130converts electrical energy to mechanical vibration energy and may be ofconventional design including piezoelectric elements, a-load mass, and ahorn structure; none of which are shown.

.T 'hetransducer 130 is received in the casing 100 in a mannersuch thatit is free -to rotate within the casing about the longitudinal axisthereof. A transducer probe 108 is attached to the transducer by meansof a thread 1510 formedon the upper end of the probe and received xinacomplementarily threaded socket 112 in the main :portion of thetransducer. The probe 108 extends downwardly throughthe reduced'portion104 and ter minates-in a point 114, which may be of conicalconfiguration as best seen in FIG. 4'of the drawings.

' rin'g, 11 6 is fixed in the end of a casing 100 by meansof a pin orthe like118 and a coil spring 120 is interposed between the ring 116 andthe upper end of the transducer 130, thereby urging the point 1 14 ofthe probe into contact with the surface of the orifice plate 18, as bestseen in FIG. 3 of the drawings.

Leads 1 12 are provided for energizing the piezoelectric elements orother driving means in the main body portion of the transducer 130 andthese leads may be a threaded outwardly through the coil spring andretaining ring 116 to any suitable source of power. The

threaded portion 106 of the end cap engages complementary threads on theclamp bar 14 to fix the casing with respect to the drop generator whilethe transducer and attached probe 108 are free to rotate with respect tothe remaining elements of the generator.

As best seen in FIGS. 3 through 5 of the drawings, the point 114 isoffset with respect to the longitudinal axis of both the probe 108 andthe casing 100. Thus, the transducer may be manually engaged throughtheopenings 124 in the casing 100 and rotated about is longitudinal axis.This will result in a shifting of the point of contact between the point114 on the probe and the upper surface of the orifice plate.

, 7 As a result, small variations between the actual and optimumcontactpointmay be compensated for after the unit has been assembled. lnthis way bending waves of the desired character may be propagated toprovide the stimulation of the filaments of the working fluid. While theform of apparatus herein described constitutes a preferred embodimentsof the invention, it is to be understood that the invention is notlimited to this precise form of apparatus, and that changes may be madetherein without departingfrom the scope of the invention. 7

What is claimed is: 1. Apparatus of the type described: a. an orificeplate having a plurality of orifices formed therethrough, b. means forsupplying a working fluid to said orifices, c. an ultrasonic transducerhaving a body portion and a tip portion, d. said tip portion'beingoffset with respect to the axis ofsaid body portion,- and v e. meansmounting said transducer for rotation about said axis thereof with 'saidtip thereof contacting said orifice plate. 2. The apparatus of claim 1wherein: a. said supplying means includes a support bar,

b. said transducer mounting means includes a transducer casing attachedto said support bar, and c. said transducer is rotatably received insaid casing and extends therefrom into contact with said orifice plate.3. The apparatus of claim 2 further comprising: a. openings definedthrough a wall of said casing, b. said transducer being accessiblethrough said openings for rotation thereof. 4. The apparatus of claim 2further comprising: a. spring means received in said casing and urgingsaid transducer into contact with said orifice plate.

5. The apparatus of claim 4 further comprising:

a. a cap mounted in one end of said casing in spaced relationship tosaid transducer, 7

b. said spring means being received in said casing between said cap andsaid'transducer.

6. The apparatus of claim 1 wherein:

8 afsaid tip portion comprises arod member attached at one end to andextending'fro'm said transducer body portion, v b. said rod memberhaving an opposite end terminating in a point in contact with saidorifice plate, c. said point being offset withrespect to the axis of isaid transducer. i 7. The apparatus of claim 6 wherein: a. said point isoffset with respect to the axis of said rod member. 8. Apparatus of thetype described comprising: a. an orifice plate having a plurality ofregularly spaced orifices formed therethrough, b. a manifoldcommunicating with said orifices, c. a support bar supporting'saidmanifold and said orifice plate, v d. means mounted on said support barfor supplying a working fluid to said manifold,

e. an elongated hollow transducer casing mounted on said support bar andextending substantially perendicular with r s ect to sai orifice lat multrason ic trans u er rotata ly receleed in said elongated transducercasing for rotation about the longitudinal axis thereof, 7

g. an elongated rod memberattached' to said transducer and extendingoutwardly of sad casing in coaxial relationship thereto,

h. said rod member terminating in a point offset with respect to thelongitudinal axis thereof,

i. said rod member extending through said manifold in noncontactingrelationship thereto and contacting said orifice plate with said point,

j. a cap member received on an outer end'of said casing,

k. a compression spring received in said casing intermediate said capmember and said transducer and urging said point into contact with saidorifice plate, and g l. openings formed in-a sidewall of said casing topermit said transducer to be engaged for rotation thereof about the axisof said casing to shift the point of contact between said rod memberpoint and said orifice plate.

1. Apparatus of the type described: a. an orifice plate having aplurality of orifices formed therethrough, b. means for supplying aworking fluid to said orifices, c. an ultrasonic transducer having abody portion and a tip portion, d. said tip portion being offset withrespect to the axis of said body portion, and e. means mounting saidtransducer for rotation about said axis thereof with said tip thereofcontacting said orifice plate.
 2. The apparatus of claim 1 wherein: a.said supplying means includes a support bar, b. said transducer mountingmeans includes a transducer casing attached to said support bar, and c.said transducer is rotatably received in said casing and extendstherefrom into contact with said orifice plate.
 3. The apparatus ofclaim 2 further comprising: a. openings defined through a wall of saidcasing, b. said transducer being accessible through said openings forrotation thereof.
 4. The apparatus of claim 2 further comprising: a.spring means received in said casing and urging said transducer intocontact with said orifice plate.
 5. The apparatus of claim 4 furthercomprising: a. a cap mounted in one end of said casing in spacedrelationship to said transducer, b. said spring means being received insaid casing between said cap and said transducer.
 6. The apparatus ofclaim 1 wherein: a. said tip portion comprises a rod member attached atone end to and extending from said transducer body portion, b. said rodmember having an opposite end terminating in a point in contact withsaid orifice plate, c. said point being offset with respect to the axisof said transducer.
 7. The apparatus of claim 6 wherein: a. said pointis offset with respect to the axis of said rod member.
 8. Apparatus ofthe type described comprising: a. an orifice plate having a plurality ofregularly spaced orifices formed therethrough, b. a manifoldcommunicating with said orifices, c. a support bar supporting saidmanifold and said orifice plate, d. means mounted on said support barfor supplying a working fluid to said manifold, e. an elongated hollowtransducer casing mounted on said support bar and extendingsubstanTially perpendicularly with respect to said orifice plate, f. anultrasonic transducer rotatably received in said elongated transducercasing for rotation about the longitudinal axis thereof, g. an elongatedrod member attached to said transducer and extending outwardly of sadcasing in coaxial relationship thereto, h. said rod member terminatingin a point offset with respect to the longitudinal axis thereof, i. saidrod member extending through said manifold in noncontacting relationshipthereto and contacting said orifice plate with said point, j. a capmember received on an outer end of said casing, k. a compression springreceived in said casing intermediate said cap member and said transducerand urging said point into contact with said orifice plate, and l.openings formed in a sidewall of said casing to permit said transducerto be engaged for rotation thereof about the axis of said casing toshift the point of contact between said rod member point and saidorifice plate.